In order to use disks > 2TB you just need to make sure you create the initial partition table in GUID format (GPT) rather than the old MS-DOS (MBR) format. You can do that using the parted command line program (using mklabel gpt) or from gparted using the 'Select new partition table type' drop down menu.
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steeldriverSep 26 '13 at 11:52

@steeldriver - Yes, GPT seems to be the trick.
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David EdwardsSep 26 '13 at 16:52

Finally, mount your array somewhere and add it to /etc/fstab if you want it to be mounted permanently. I did this:

Create a location to mount the array at by running sudo mkdir /mnt/md0.

Edit /etc/fstab and add the following line:

/dev/md0 /mnt/md0 auto defaults 0 0

Mount by running sudo mount /mnt/md0.

Now you can start using your array. Bear in mind, however, that before it is fully operation it will need to complete its initial sync. You can track its progress by running sudo mdadm --detail /dev/md0.